Many traditional energy sources, such as e.g. fossil fuels, are being depleted faster than new ones are being made. Fossil fuels are non-renewable resources because they take millions of years to form. Also, use of fossil fuels raises serious environmental concerns. Renewable energy sources represent a promising alternative to many traditional energy sources. Biomass represents one source of renewable energy.
If biomass energy is to have a long-term, commercial future, the organic material must be processed to generate affordable, clean and efficient energy forms, such as liquid and gaseous fuels, or electricity. Biomass processing is important to ensure an efficient exploitation of the biomass energy. However, the energy potential can often be difficult to exploit. An increased exploitation of the energy potential of a biomass may result in an increased production of renewable energy sources, such as biogas.
Additionally, spent biomass materials having a reduced organic nitrogen content can be upgraded, sanitized and re-used in the production of many edible products.
Extensive scientific and engineering work has been conducted on the biogasification of waste materials. The fundamental technique relies on an anaerobic digestion or fermentation process. However, anaerobic microorganisms responsible for methanogenesis are inhibited by ammonia and methanogenesic anaerobic bacteria are inhibited by and cease to metabolise nutrients effectively at high ammonia concentration levels.
The problems associated with ammonia inhibition have made currently available technical solutions difficult to operate—especially when using biomasses containing relatively high amounts of nitrogen.
To mitigate these problems, it has been attempted to control the carbon to nitrogen (C/N) ratio of the biomass material subjected to fermentation. However, state-of-the-art solutions continue to suffer from a number of disadvantages. For example, adjusting the ammonia concentration in a reactor by adjusting the C/N ratio of the biomass is a slow process, and adjusting the C/N ratio may prove insufficient when handling biomasses prone to generating relatively high ammonia concentrations during anaerobic digestion.
Lime pressure cooking and ammonia stripping has been disclosed as a way to reduce the amount of organic and inorganic nitrogen present in a biomass to be subjected to anaerobic fermentation. Reference is made e.g. to U.S. Pat. No. 7,883,884.
Furthermore, many complex biomasses contain macromolecular constituents which are difficult to metabolize for microbial organisms traditionally involved in the production of biogas. In particular, macromolecular constituents, such as cellulose, hemicellulose, lignocellulose and lignin, are present in many biomass materials and can only be metabolized to a limited extent during a biogas fermentation process.
There is a need for improved and more cost effective pre-treatment methods for rendering the afore-mentioned, recalcitrant biomass material constituents more accessible for many microbial organisms present during different stages of a biogas production.